In general, an air intake system for a vehicle includes an air cleaner, a turbo-charger, an inter-cooler, an air duct and an engine manifolder, and outdoor air introduced into an internal combustion engine by the air intake system repeats expansion and compression, causing pulsation. This pulsation effect causes noise due to the pressure changes of air, and it is especially the cause of greater noise by a resonation effect of air in the vehicle itself or interior space of the vehicle.
To suppress air intake noise, an air intake hose installed at the rear end of the turbo-charger has a resonator to tune the air intake system to a specific frequency.
The conventional resonator primarily includes a Helmholtz resonator that reduces noise in air by reducing the sound pressure of a specific frequency range in noise generating from the air intake system. That is, the Helmholtz resonator reduces noise in air introduced into the inside by tuning and resonating air intake noise of a specific frequency, in particular, a low frequency.
However, when a high load is applied to the engine of the vehicle or the vehicle speeds up, as exhaust gas discharged from the vehicle increases, the revolutions per minute (RPM) of the turbo-charger increases, and accordingly, an amount of air introduced into the turbo-charger and an air intake pipe line increases, and the temperature and pressure increases. This change of condition changes an area in which noise occurs, and at the same time, changes a noise reduction frequency range of a noise attenuator designed of a fixed type.
To solve this problem, Korean Patent Publication No. 2011-0048931 discloses an air intake noise attenuator wherein a resonation chamber for reducing air intake noise is divided into a plurality of parts, a plurality of slits communicating with the resonation chambers is provided, and air with a specific frequency is tuned for each resonation chamber. Because the air intake noise attenuator is configured such that tuning frequency of air is different for each resonation chamber, an advantage is that it can tune and resonate air with many frequencies.
However, air transmitted from the turbo-charger to the resonator is not limited to a preset specific frequency, and air with a continuous frequency is continuously transmitted. Accordingly, even though the air intake noise attenuator is applied to the internal combustion engine, it is only possible to tune a specific frequency in many bands, and it is impossible to tune an analogous type continuous frequency of air.